Iminoboranes structure

The structure of compound (X) was confirmed by its i.r. and n.m.r. spectrum. However, such a transformation as exemplified by Eq. (35) is not consistent with the tendency to retain the iminoborane structure which is predominant even in compounds containing more mobile BH groups (c.f. Eq. (8) also c.f. Sect. II). 

In contrast to more recent publications but remaining consistent with the previous volumes in the boron series, the iminoborane structure is written as B=N and not as B=N. In fact, the real electronic structure is more realistically symbolized by B=N [3], but it seems reasonable to avoid =NR, in accord with the commonly accepted Iminoborane nomenclature. Publications of the current literature often use RB=NR for iminoboranes [6,12,13,17, 22, 35] consequently, the aminoborane structure in these publications Is written as R2B=NR2 instead of R2B-NR2 [4, 7,14]. For iminoboranes, formulations including arrows [38], showing triple bonds, RB NR [3], or dotted lines [10] have been used, while for amino-iminoboranes the formulation RN = B—NR2 seems to be preferred In the relevant reviews [3, 39]. 

In contrast to more recent publications but remaining consistent with the previous volumes of the Boron Series, the iminoborane structure is written as B=N and not as B=N. In fact, the real electronic structure is more realistically symbolized by B=N, but it seems reasonable to avoid =NR in accordance with the commonly accepted iminoborane nomenclature. 

The finding of preparatively available iminoboranes RB = NR some years ago opened exciting new possibilities not only in B—N chemistry, but also in coordination chemistry. The first examples of iminoborane-transition-metal complexes have now been published. The structurally completely characterized t-BuB = NBu-t adds, like its alkyne analog, to the 03(00)5 fragment as a bridging ligand. When Co2(CO)g and t-BuB = NBu-t are dissolved in pentane at 0°C, warming to RT and evaporation of unreacted iminoborane yields (t-BuBNBu-t)Co2(CO)5 (86%) as a black solid, which can be recrystallized from ether-nitromethane (1 3) ... 

Most of the monomeric compounds are highly reactive liquids and are rapidly hydrolysed by atmospheric moisture. In the monomeric iminoboranes the N-B bond order is greater than unity and these compounds represent an allene-type system with cumulated multiple bonds as indicated by structure (I) 3S). 

Infrared spectroscopy is an excellent tool in iminoborane chemistry, which readily permits, to distinguish between iminoboranes and nitrile-borane adducts and to identify monomeric and dimeric forms of iminoboranes. This event is due to the fact that the i>CN of CN multiple bonds absorbs outside the fingerprint region and can be considered to be a valuable group frequency even when mixed with other vibrational modes. In some cases other vibrations like NH, BH, B-halogen or B-S stretching modes are helpful for determining the structure of iminoboranes. 

Monomeric iminoboranes exhibit a B-N bond order higher than unity due to p - p bonding between nitrogen and three-coordinate boron. This event results in an allene-type structure as shown in (I) exhibiting its antisymmetric stretching vibration around 1800 cm-1. This should have a predominant i>(CN) character, whereas in the symmetric mode of lower wavenumber the B-N charac-... 

In particular, iminoboranes (XBNR) are isoelectronic with alkynes (XCCR). Well-known comparable pairs of isoelectronic species are aminoboranes (X2BNR2) and alkenes (X2CCR2), amine-boranes (X3BNR3) and alkanes (X3CCR3), borazines [(XBNR)3] and benzenes [(XCCR)3], etc. The structure of aminoboranes, amine-boranes, and borazines is well known from many examples. It has turned out that these BN species are not only isoelectronic, but also have structures comparable with the corresponding CC species. In the case of borazines, the aromatic character was widely discussed on the basis of theoretical and experimental arguments. The structural and physical properties of... 

This article describes what is known about the formation, structure, and reactivity of iminoboranes. The chemistry of iminoboranes is in its beginnings, and so we cannot paint a complete picture. A comparison between iminoboranes and the corresponding alkynes will serve as a background throughout this novel field of boron chemistry. 

Apparently there is a substantial contribution to the B—N bond of HBNH from one a- and two orthogonal 7i-bonds. Expressed in simple terms, there is a B=N triple bond in iminoboranes. Concerning a structural formula for HBNH, the real situation is represented best by H—B=N—H. 

It can be concluded from the discussions in Sections IIIA-D that B=N double bonds in aminoboranes and B N triple bonds in iminoboranes represent a realistic picture. It is here recommended, therefore, to indicate these bonds in structural formulas as usual, but to omit erroneous formal charges, e.g., amine-borane X3B—NR3 aminoborane X2B=NR2i iminoborane XB=NR. [Note that R3N-BX3 is recommended as the correct molecular formula for amine-boranes (46), but one is not bound to rules in constructing structural formulas, e.g., X3B—NR3.]... 

Efforts to add Lewis acids to dialkyliminoboranes R BNR were not so successful, aa would be expected, since betaine structures of the type R B=NR—A with an unfavorable linear sextet boron atom would be formed (19, 33). Equation (26) is restricted to iminoboranes XBNR with a 7i-electron donating group X. 

In the infant chemistry of iminoboranes only one example of insertion into a bridge position has been found [Eq. (56)] (86). That the structure of the product [Eq. (56)] corresponds to structure Xlla has been deduced from the CO absorption bands in the IR spectra, which... 

Iminoboranes (continued) in transition metal complexes, 31 165-167 X-ray structural studies, 31 135 Iminofluorosulfinamide ions, 19 206-208 Iminofluorosulfonylamide ions, 19 200 Iminolithium complexes, solid-state structures, 37 67-75 dimers, 37 68-70 trimers, 37 68-70... 

Properties and Reactions. The structure of (alkyl)iminoboranes RB=NR is characterized by a linear C—B—N—C geometry and a B—N bond order approaching three. Amino iminoboranes can be described using three resonance structures ... 

The iminoborane. /-PrBsN-f-Bu. trimerizes to (/-PrBN-t-Bu), which has a Dewar-borazmc type stmeture.174 Compare (his structure to that of borazine. 

The iminoborane, i-PrB=N-/-Bu, trimerizes to (i-PrBN-/-Bu)j which has a Dewar-borazine type structure.174 Compare this structure to that of borazine. 

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